Extremely dissatisfied customer

I had a data contract with Cell C which ended on 26 Jan 2023. The cancellation took effect on 06 February which was the last day I was able to access the data and the contract was cancelled. I have since received a bill charging me for the whole month of February at double the amount, taking into account that I only had use of the facility for a total of 6 days out of 28. I have tried to call the call center on numerous occasions, but up until now I have had absolutely no joy what so ever. No one can understand my concern. Why am I not being charged pro rata? This is ******* as I am not utilising their services but still being charged. I have requested that management contact me as this is not acceptable by any standard.